The present invention relates to an optical apparatus, and a manufacturing method therefor, for use in, for example, a reflection type display unit which uses deposition/dissolution of metal and which is employed in place of an electrochromic display unit to display characters or numerics or an X-Y matrix display or the like and in an optical filter which is capable of controlling light transmittance in a visible light region (wavelength 1=400 nm to 700 nm).
Hitherto, an electrochromic device (hereinafter called an "ECD") which has been employed in a digital clock or the like is a non-luminous display unit using reflected light or transmitted light. Therefore, an advantage can be obtained in that fatigue can be prevented even if observation is performed for a long time. Moreover, advantages can be obtained in that a relatively low operating voltage is required and power consumption can be reduced. For example, a liquid ECD disclosed in Japanese Patent Laid-Open No. 59-24879 has been known, the foregoing liquid ECD being composed of an EC material which is an organic viologen molecule derivative which reversibly realizes a coloring/decoloring state.
However, the ECD composed of the viologen molecule derivative has a problem of unsatisfactorily low response speed and an insufficient shielding characteristic.
Therefore, a reflection type dimmer using deposition/dissolution of metal salts has attracted attention in place of the ECD. Thus, an electrochemical dimmer using deposition/dissolution of silver has been researched and developed.
FIGS. 13A, 13B and 14 show the structure of a cell of the foregoing conventional electrochemical dimmer.
As shown in FIGS. 13A and 14, a pair of transparent glass substrates 24 and 25 serving as display windows are disposed apart from each other for a predetermined distance. As shown in FIG. 13A, opposite working electrodes 22 and 23 made of ITO (Indium Tin Oxide prepared by doping tin into indium oxide) are disposed on the inner surfaces of the substrates 24 and 25. Silver-salt solution 21 is placed between the opposite working electrodes 22 and 23. Reference numeral 26 represents a counter electrode in the form of a silver plate disposed between the outer peripheries of the substrates 24 and 25 and also serving as a spacer.
The silver-salt solution 21 is prepared by dissolving silver bromide in dimethyl sulfoxide (DMSO). As shown in the drawing, the counter electrode 26 is disposed as an anode and the working electrodes 22 and 23 are disposed as a cathode. When a DC operating voltage is applied between the cathode and anode for a predetermined time, the following oxidation-reduction reactions occur on the cathode: EQU Ag.sup.+ +e.sup.-.fwdarw.Ag
The obtained deposits of Ag cause the working electrodes 22 and 23 serving as the cathode to be converted from a transparent state to a coloring state. FIG. 13B is a diagram showing the principle of the above-mentioned phenomenon.
Since Ag is deposited on the working electrodes 22 and 23 as described above, specific color (for example, reflected light) caused from the deposited Ag can be observed through the display window. The filtering effect caused from coloring, that is, the transmittance of visible light (the depth of color) is changed in accordance with the level of the voltage or time for which the voltage is applied. Therefore, control of the voltage or the time enables the foregoing cells to act as the transmittance-variable display devices or optical filters.
When a DC voltage is applied between the counter electrode 26 and the working electrodes 22 and 23 in a direction opposite to the above-mentioned process, the working electrodes 22 and 23, on which Ag has been deposited, serve as an anode. Thus, the following reactions occur: EQU Ag.fwdarw.Ag.sup.+ +e.sup.-
As a result, Ag deposited on the working electrodes 22 and 23 is dissolved in the silver-salt solution 21. Thus, the state of the colored working electrodes 22 and 23 is changed from the colored state to a transparent state.
FIGS. 15 and 16 show another electrochemical dimming device. In this example, a pair of transparent glass substrates 4 and 5 forming a cell are disposed apart from each other by a predetermined distance as shown in FIG. 15 which is a cross sectional view. Pairs of working electrode 2a, 2b, 2c, 2d and 2e and 3a, 3b, 3c, 3d and 3e each of which is made of ITO and which are disposed opposite to one another are formed on the inner surfaces of the substrates 4 and 5. Counter electrodes 7a and 7b in the form of silver plates are disposed on the outer peripheries of the working electrodes 2a to 2e and 3a to 3e. The substrates 4 and 5 are disposed apart from each other by a predetermined distance by a spacer 6. Silver-salt solution 1 is enclosed between the substrates 4 and 5.
As shown in FIG. 16 which is a plan view, the working electrodes 2a to 2e and 3a to 3e and the counter electrodes 7a and 7b are formed into a concentric pattern. The electrodes 2a and 3a, 2b and 3b, 2c and 3c, 2d and 3d, 2e and 3e and 7a and 7b are connected to operating power sources 8a, 8b, 8c, 8d, 8e and 8f through electric lines 9a, 9b, 9c, 9d, 9e and 9f in the form of thin chrome wires.
When predetermined potentials (V.sub.1, V.sub.2, V.sub.3, V.sub.4 and V.sub.5, while V.sub.6 is a referential potential at the counter electrodes 7a and 7b) are applied between opposite working electrodes 2a and 3a, 2b and 3b, 2c and 3c, 2d and 3d and 2e and 3e, silver can be deposited from the silver-salt solution 1 on each electrode which is the cathode. Thus, color can be developed. The transmittance of visible light (or the density of color) is changed in accordance with the level of the voltage or time for which the voltage is applied.
When the voltages are made such that V.sub.1 =V.sub.2 =V.sub.3 =V.sub.4 =V.sub.5, color can be developed in the overall region of the cell. Moreover, the density can uniformly be changed in accordance with the voltage or the time for which the voltage is applied. When the voltages are made such that, for example, .vertline.V.sub.1.vertline.&lt;.vertline.V.sub.2.vertline.&lt;.vertline.V.sub. 3.vertline.&lt;.vertline.V.sub.4.vertline.&lt;.vertline.V.sub.5.vertline., the density of the color is raised from the center to the periphery (that is, the transmittance is reduced). When the voltages are made such that .vertline.V.sub.1.vertline.&gt;.vertline.V.sub.2.vertline.&gt;.vertline.V.sub. 3.vertline.&gt;.vertline.V.sub.4.vertline.&gt;.vertline.V.sub.5.vertline., the transmittance is enlarged from the center to the periphery. The above-mentioned structure is effective to serve as an optical diaphragm for a CCD (Charge Coupled Device) for a TV camera or the like. The structure is able to sufficiently raise the density of integration of the CCD.
The above-mentioned electrochemical dimming device has a problem that the cost cannot be reduced because raw metal plates, such as the raw silver plates, are employed as it is to serve as the counter electrodes, 7a, 7b and 26. Since the lifetime of the device has been enlarged, there arises another problem in that silver particles inactivated and deposited on the counter electrode float in the silver-salt solution. Thus, the inside portion of the device is contaminated, causing the transmittance, which is realized when the device is in the transparent state, to deteriorate. Moreover, the electrodes are short-circuited.
When decoloring of the working electrodes of the device shown in FIGS. 15 and 16 is performed, silver is deposited on the counter electrodes 7a and 7b which are the cathode. At this time, electric lines of force of the electric field are concentrated to sharp portions of the electrodes, as shown in FIG. 17 (for example, 7b is shown). It leads to a fact that silver is enlarged into grains each having a relatively large size and deposited in the foregoing portions. The granular silver A is, differently from silver B in the form of a thin film, not easily be dissolved when color is developed on the working electrodes. Therefore, the silver A is separated and allowed to float in the silver-salt solution 1 while the granular and inactive state is maintained. If the inactive silver particles are increased in the silver-salt solution, the transparency of the device deteriorates when decoloring is performed on the working electrodes. What is worse, the silver particles cause the electrodes to be short-circuited.